In vitro Investigation of Platelet Dysfunction Induced by Osmotic Pressure Variations

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Background: Severe variations in osmotic pressure are significant contributors to critical patient morbidity and mortality and might also affect platelet volume. We aimed to investigate possible osmotic-induced changes in mean platelet volume (MPV) and their possible effects on platelet aggregation activity (PLAG). Methods: We induced experimental variations of serum osmolality in blood samples from healthy volunteers (heparinized whole blood [WB]) and isolated platelets (platelet-rich plasma [PRP]) by adding isotonic, hypertonic, and hypotonic solutions of saline/water (pH = 7.2–7.4). PLAG was tested in WB samples with impedance aggregometry (IA) and in PRP samples with light transmission aggregometry (LTA) using three agonists: adenosine diphosphate (ADP, 10 μ<sc>m</sc>), thrombin receptor activating peptide (TRAP-6, 10 μ<sc>m</sc>), and arachidonic acid (500 μ<sc>m</sc>). Osmolality was either calculated using a formula or measured directly. Results: We found almost identical osmolalities in WB and PRP preparations. Osmotic stress did not produce significant changes in MPV. In IA testing, the hypotonic challenge of WB preparations produced significant reductions at 50% (p = 0.056) (95% CI: 11.2–2.4, in Ohms) of ADP and at 31% (p = 0.017) (95% CI: 13.4–8.6, in Ohms) of TRAP-6-induced PLAG, respectively. In PRP, we did not observe any variations in PLAG with LTA. Conclusions: We conclude that in vitro hypotonic stress of WB samples has an inhibitory effect on the PAR-1 (TRAP-6-induced) pathway and on the P2Y₁₂ (ADP-induced) pathway and reflects a distinct in vivo effect of hypoosmotic stress on WB human platelet preparations.